Optical magnifier suitable for use with a microdisplay device

ABSTRACT

An optical magnifier is provided. One general form of one example embodiment includes two lens elements, at least two aspheric surfaces, and at least one diffractive surface. Another general form of another example embodiment includes three lens elements, and at least three aspheric surfaces. At least two of the aspheric surfaces can be simple conics. The optical magnifier, suitable for use in an electronic display system, has an apparent field of view of at least +/−10 degrees; a magnification of at least 15×; a back focal length of at least 5 mm; and an eye relief greater than the effective focal length of the optical magnifier. The lens elements can be made from plastic.

FIELD OF THE INVENTION

This invention relates generally to optical systems and in particular tooptical magnifiers incorporated into and/or used in conjunction withother optical components.

BACKGROUND OF THE INVENTION

Optical Magnifiers (also referred to as “eyepieces” or “loupes”) areknown. Typically, these optical devices are used to allow direct viewingof slides or other small objects or are used as part of other opticalsystems such as, for example, telescopes and viewfinders.

Conventional optical magnifiers utilize magnifier lenses that provide anenlarged virtual image of a real object in front of a viewer's eye. Itis generally preferable that such lenses, in combination with the objectbeing viewed, provide an apparent field of view to the user in excess of+/−10 degrees, in order to avoid the sensation of “tunnel vision”.Additionally, these magnifier lenses preferably provide a relativelylong eye relief (that is, the distance at which the lens can be heldfrom the eye) in order to allow an object to be comfortably viewed.

Optical magnifiers have also been suggested for viewing electronicdisplays incorporated, for example, in portable electronic devices. Whenused to view electronic displays, the same criteria, described above,applies, even though newer high quality micro-displays are now beingmanufactured with full diagonals of 6 mm or less. In order to obtain a+/−10 degree apparent field of view, such small micro-displays require ahigh magnification lens (on the order of 15× or greater), whichtranslates to an effective focal length of approximately 17 mm or less.As is known, magnification for this type of optical system is calculatedusing the standard formula: M=254 mm/EFL, where EFL is the effectivefocal length of the lens, measured in mm.

For comfortable viewing by users, including those wearing eyeglasses, itis generally accepted that a reasonable eye relief is approximately 17mm or greater. As such, in the relative sense, the eye relief shouldpreferably be at least as great as the EFL of the lens (for example, 17mm in the 15× example described above) for micro-displays of this size.This relationship between eye relief and EFL becomes even more of aconcern when shorter focal length (higher magnification) systems arecontemplated. This is a new and challenging goal that did not previouslyexist for larger electronic displays used with correspondingly lowermagnification lenses.

In U.S. Pat. No. 4,094,585, E. I. Betensky discloses a three-elementall-plastic optical magnifier comprising from the viewing end, a firstpositive lens group comprising a single element, and a second lens groupcomprising a bi-convex element and a bi-concave element forming adoublet having the overall shape of a meniscus. This magnifier has amagnification in the range of 13× to 14×. For micro-displays with filldiagonals of less than 6 mm, this magnifier does not provide the desired+/−10 degree field of view. Additionally, this magnifier has the addedlabor expense of cementing two elements to form a doublet, which may beunacceptable for cost-sensitive applications.

In U.S. Pat. No. 5,835,279, I. Marshall and R. Holmes disclose athree-clement all-plastic magnifier lens for viewing an LCD in thebinocular vision system of a head-mounded display unit. This design hasa large (+/−35.8 degree) apparent field of view and a long (17 mm) eyerelief. However, the LCD is quite large (33.65 mm full diagonal) and theresulting magnification is only about 11×, making it unsuitable for usewith micro-displays of the scale contemplated here. Additionally, whenthis system is scaled to a magnification of 15×, the eye relief drops toabout 12.4 mm, quite short for users wearing eyeglasses.

In U.S. Pat. Nos. 5,909,322 and 5,886,825, J. R. Bietry discloses two-and three-element plastic designs for magnifier lenses suitable for usein liquid crystal (LCD) or light emitting diode (LED) micro-displaysystems. Although these lenses have a magnification of 16×, high imagequality, and long eye relief, these designs contain at least onediffractive surface, for both the two element and three element formsand/or include a rear meniscus lens which is concave toward the objectand positionable within 5 mm of the object surface. As a number of newer“micro-display” devices, for example, LCD devices, depend on light beingdelivered from the front of the display via a polarizing beam splittingdevice, a back focal length (BFL) of the lens in excess of 5 mm is oftenessential for the placement of the optical magnifier. For micro-displayswhich require a BFL in excess than 5 mm, these designs will simply notfunction.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a magnifier lenscomprises in order from an eye side a first positive power meniscus lenselement having an eye side surface and an object side surface with atleast one of the eye side surface and the object side surface isaspheric; and a second positive power lens element having an asphericobject side surface convex toward the object side and an eye sidesurface, wherein at least one of the object side surface of the firstpositive power meniscus element and the eye side surface of the secondpositive power element is diffractive.

According to another aspect of the invention, an optical systemcomprises in order from an eye side a first positive power meniscus lenselement having an eye side surface and an object side surface with atleast one of the eye side surface and the object side surface beingaspheric; a second positive power lens element having an aspheric objectside surface convex toward the object side and an eye side surface,wherein at least one of the object side surface of the first positivepower meniscus element and the eye side surface of the second positivepower element is diffractive; and an object to be viewed.

According to another aspect of the invention, a magnifier lens comprisesin order from an eye side a first positive power lens element having anaspheric eye side surface; a second negative power meniscus lens elementhaving an aspheric object side surface; and a third positive powerbi-convex lens element having at least one aspheric surface.

According to another aspect of the invention, an optical systemcomprises in order from an eye side a first positive power lens elementhaving an aspheric eye side surface; a second negative power meniscuslens element having an aspheric object side surface; a third positivepower bi-convex lens element having at least one aspheric surface; andan object to be viewed.

According to another aspect of the invention, a magnifier lens comprisesin order from an eye side a first positive power lens element having anaspheric surface; and a second positive power lens element having anaspheric surface, the magnifier lens having a back focal length in air,wherein the back focal length of the magnifier lens in air is greaterthan 5 mm.

BRIEF DESCRIPTION OF THE DRAWINGS

In the detailed description of the preferred embodiments of theinvention presented below, reference is made to the accompanyingdrawings, in which:

FIG. 1 shows a sectional view of a first embodiment of the magnifierlens system of the first general form;

FIG. 2 shows a sectional view of a second embodiment of the magnifierlens system of the first general form;

FIG. 3 shows a sectional view of a third embodiment of the magnifierlens system of the first general form;

FIG. 4 shows a sectional view of a fourth embodiment of the magnifierlens system of the first general form;

FIG. 5 shows a sectional view of a first embodiment of the magnifierlens system of the second general form;

FIG. 6 shows a sectional view of a second embodiment of the magnifierlens system of the second general form;

FIG. 7 shows a sectional view of a third embodiment of the magnifierlens system of the second general form;

FIG. 8 shows a plot of the through-focus Modulation Transfer Function(MTF) of the magnifier lens illustrated in FIG. 1, the MTF ispolychromatic (with equal weights of 510, 560, 610 nm light) at aspatial frequency of 21 line pairs/mm;

FIG. 9 shows a plot of the through-focus Modulation Transfer Function(MTF) of the magnifier lens illustrated in FIG. 2, the MTF ispolychromatic (with equal weights of 510, 560, 610 nm light) at aspatial frequency of 21 line pairs/mm;

FIG. 10 shows a plot of the through-focus Modulation Transfer Function(MTF) of the magnifier lens illustrated in FIG. 3, the MTF ispolychromatic (with equal weights of 510, 560, 610 nm light) at aspatial frequency of 21 line pairs/mm;

FIG. 11 shows a plot of the through-focus Modulation Transfer Function(MTF) of the magnifier lens illustrated in FIG. 4, the MTF ispolychromatic (with equal weights of 510, 560, 610 nm light) at aspatial frequency of 21 line pairs/mm;

FIG. 12 shows a plot of the through-focus Modulation Transfer Function(MTF) of the magnifier lens illustrated in FIG. 5, the MTF ispolychromatic (with equal weights of 510, 560, 610 nm light) at aspatial frequency of 21 line pairs/mm;

FIG. 13 shows a plot of the through-focus Modulation Transfer Function(MTF) of the magnifier lens illustrated in FIG. 6, the MTF ispolychromatic (with equal weights of 510, 560, 610 nm light) at aspatial frequency of 21 line pairs/mm; and

FIG. 14 shows a plot of the through-focus Modulation Transfer Function(MTF) of the magnifier lens illustrated in FIG. 7, the MTF ispolychromatic (with equal weights of 510, 560, 610 nm light) at aspatial frequency of 21 line pairs/mm.

DETAILED DESCRIPTION OF THE INVENTION

The present description will be directed in particular to elementsforming part of, or cooperating more directly with, apparatus inaccordance with the present invention. It is to be understood thatelements not specifically shown or described may take various forms wellknown to those skilled in the art.

In the following descriptions of example embodiments of the invention,the term magnifier lens is used to describe an optical system. However,a person skilled in the art will understand that the magnifier lens(s)described herein can be used as, for example, an eyepiece with otheroptical components. As such, the term magnifier lens should not beconsidered limited to any particular application. Note, that since thatlight can be directed through the magnifier lens in any direction, theeye position can be replaced by a galvanometer or a rotating polygonwith some minor distortion adjustments. Thus, a magnifier lensconstructed according to the present invention can be used, for example,in scanner applications. The magnifier lens can also be used as part ofa viewfinder system in, for example, a digital or hybrid (digital/film)camera to image a scene displayed on an electronic display to a user'seye for preview and/or review.

Referring to FIGS. 1-7, the terms “front” and “rear” refer to the eyeside and object side of the magnifier lens, respectively. In thefollowing examples, 10 is the diaphragm of an eye or other instrument,20 is a polarizing beam splitter (PBS) or other suitable device fordividing light rays, and 30 is a cover plate protecting an object to beviewed (for example, an image display) 40. The PBS 20 is preferably apartially transmissive/partially reflective device used to illuminatethe display front-on via a light source located out of the optical pathof the magnifier. Typically, in practice, the PBS 20 (or other beamsplitting device, or other light dividing device, etc.) is onlynecessary for objects to be viewed (for example, image displays) 40 thatrequire front-on illumination.

Although the PBS 20 is shown here as perpendicular to the optical axis60 of the optical system 50, the PBS 20 is typically tilted at someangle or curved along at least one dimension or both. Additionally, thecorrection of aberrations due to this non-axially symmetric componentwould require at least one additional non-axially symmetric feature orcomponent. For these reasons, and with simplicity and cost of theoptical system 50 in mind, no attempt to correct aberrations associatedwith the PBS was made other than inserting the PBS 20 as a thin flatplate oriented perpendicular to the optical axis 60.

The example embodiments of the invention are illustrated in FIGS. 1-7,and Tables 1-7, respectively. In FIGS. 1-7 and Tables 1-7, the surfaceradii R are numbered beginning at the front side of the magnifier lens70 ending at the surface of the object to be viewed (for example, animage display surface) 40. In Tables 1-7, the thicknesses of the lenselements and the airspaces between the lens elements are both labeled as“thickness” and are listed on the same line as the surface preceding thethickness. For example, the first thickness in Table 1 corresponds tothe distance from the eye diaphragm to the first surface of the firstelement E₁. Similarly, the second thickness in Table 1 corresponds tothe thickness of the first element E₁ in the system. All thicknessesprovided in Tables 1-7 are in millimeters. All indices and V-numbers(also known as Abbe numbers) are for the helium d line of the spectrumat a wavelength of 587:6 nm. Additionally, the example embodiments arecolor-corrected for the visible spectrum by modeling the photopicresponse of the human eye using equal weights of 510, 560, and 610 nmlight.

A magnifier lens 70 of a first example embodiment is depicted in FIG. 1.This magnifier lens 70 includes two lens elements E₁ and E₂. The firstlens element E₁ is a positive power meniscus element concave toward therear, object side. The front, eye side surface of element E₁ is asphericand the rear, object side surface of element E₁ is spherical. The secondlens element E₂ is a positive power meniscus lens element as well. Thefront, eye side surface of element E₂ is a diffractive and the rear,object side surface of element E₂ is aspheric. Elements E₁ and E₂ aremade of plastic and can be molded. The total thickness of the magnifierlens 70, including elements E₁ and E₂ and the airspace between them, isabout 8.6 mm. The total thickness from the front, eye side surface of E₁to the surface of the object to be viewed (for example, an image displaysurface) 40 is about 16.7 mm.

A magnifier lens 70 of a second example embodiment is depicted in FIG.2. This magnifier lens 70 includes two lens elements E₁ and E₂. Thefirst lens element E₁ is a positive power meniscus element concavetoward the rear, object side. The front, eye side surface of element E₁is spherical and the rear, object side surface of element E₁ isaspheric. The second lens element E₂ is a positive power meniscus lenselement as well. The front, eye side surface of element E₂ is adiffractive and the rear, object side surface of element E₂ is aspheric.Elements E₁ and E₂ are made of plastic and can be molded. The totalthickness of the magnifier lens 70, including elements E₁ and E₂ and theairspace between them, is about 8.6 mm. The total thickness from thefront, eye side surface of E₁ to the surface of the object to be viewed(for example, an image display surface) 40 is about 16.9 mm.

A magnifier lens 70 of a third example embodiment is depicted in FIG. 3.This magnifier lens 70 includes two lens elements E₁ and E₂. The firstlens element E₁ is a positive power meniscus element concave toward therear, object side. The front, eye side surface of element E₁ is asphericand the rear, object side surface of element E₁ is diffractive. Thesecond lens element E₂ is a positive power meniscus lens element aswell. The front, eye side surface of element E₂ is spherical and therear, object side surface of element E₂ is aspheric. Elements E₁ and E₂are made of plastic and can be molded. The total thickness of themagnifier lens 70, including these two elements and the airspace betweenthem, is about 8.1 mm. The total thickness from the front, eye sidesurface of E₁ to the surface of the object to be viewed (for example, animage display surface) 40 is about 16.2 mm.

A magnifier lens 70 of a fourth example embodiment is depicted in FIG.4. This magnifier lens 70 includes two lens elements E₁ and E₂. Thefirst lens element E₁ is a positive power meniscus element concavetoward the rear, object side. The front, eye side surface of element E₁is aspheric and the rear, object side surface of element E₁ isdiffractive. The second lens element E₂ is a positive power bi-convexlens element. The front, eye side surface of element E₂ is spherical andthe rear, object side surface of element E₂ is aspheric. Elements E₁ andE₂ are made of plastic and can be molded. The total thickness of themagnifier lens 70, including these two elements and the airspace betweenthem, is about 8.4 mm. The total thickness from the front, eye sidesurface of E₁ to the surface of the object to be viewed (for example, animage display surface) 40 is about 16.5 mm.

A magnifier lens 70 of a fifth example embodiment is depicted in FIG. 5.This magnifier lens 70 includes three lens elements E₁, E₂, and E₃. Thefirst lens element E₁ is a positive power bi-convex element. The front,eye side surface of element E₁ is aspheric (simple conic) and the rear,object side surface of element E₁ is spherical. The second lens elementE₂ is a negative power meniscus lens element convex toward the eye side.The front, eye side surface of element E₂ is spherical and the rear,object side surface of element E₂ is aspheric (simple conic). The thirdlens element E₃ is a positive power bi-convex element. The front, eyeside surface of element E₃ is spherical and the rear, object sidesurface of element E₃ is aspheric. Elements E₁, E₂, and E₃ are made ofplastic and can be molded. The total thickness of the magnifier lens 70,including these three elements and the airspaces between them, is about9.8 mm. The total thickness from the front, eye side surface of E₁ tothe surface of the object to be viewed (for example, an image displaysurface) 40 is about 17.9 mm.

A magnifier lens 70 of a sixth example embodiment is depicted in FIG. 6.This magnifier lens 70 includes three lens elements E₁, E₂, and E₃. Thefirst lens element E₁ is a positive power meniscus element, convextoward the eye side. The front, eye side surface of element E₁ isaspheric and the rear, object side surface of element E₁ is spherical.The second lens element E₂ is a negative power meniscus lens elementconvex toward the eye side. The front, eye side surface of element E₂ isspherical and the rear, object side surface of element E₂ is aspheric(simple conic). The third lens element E₃ is a positive power bi-convexelement. The front, eye side surface of element E₃ is spherical and itsrear, object side surface is aspheric. Elements E₁, E₂, and E₃ are madeof plastic and can be molded. The total thickness of the magnifier lens70, including these three elements and the airspaces between them, isabout 9.5 mm. The total thickness from the front, eye side surface of E₁to the surface of the object to be viewed (for example, an image displaysurface) 40 is about 17.2 mm.

A magnifier lens 70 of a seventh example embodiment is depicted in FIG.7. This magnifier lens 70 includes three lens elements E₁, E₂, and E₃.The first lens element E₁ is a positive power bi-convex element. Thefront, eye side surface of element E₁ is aspheric (simple conic) and therear, object side surface of element E₁, is spherical. The second lenselement E₂ is a negative power meniscus lens element convex toward theeye side. The front, eye side surface of element E₂ is spherical and therear, object side surface of element E₂ is aspheric (simple conic). Thethird lens element E₂ is a positive power bi-convex element. The front,eye side surface of element E₃ is aspheric and the rear, object sidesurface of element E₃ is spherical. Elements E₁, E₂, and E₃ are made ofplastic and can be molded. The total thickness of the magnifier lens 70,including these three elements and the airspaces between them, is about9.3 mm. The total thickness from the front, eye side surface of E₁ tothe surface of the object to be viewed (for example, an image displaysurface) 40 is about 17.6 mm.

The seven example embodiments described above are designed for an objectsemi-diagonal of 2.4 mm. These embodiments have effective focal lengthsbetween 12.87 mm and 13.05 mm and corresponding magnifications between19.7× and 19.5×, respectively. Embodiments 1-7 have an apparent field ofview of +/−10.5 degrees, an eye relief of 17 mm, and assume a pupildiameter of 6 mm. The resulting relative aperture of embodiments 1-7 isabout f/2.2. The seven example embodiments have a maximum distortion(absolute value) <1% and a primary lateral chromatic aberration(absolute value)<3 microns. Additionally, any one or all of theindividual lens elements described above can be made using glass inconjunction with a grinding and polishing or molding manufacturingprocess.

The embodiments described above are suitable for use with LCD-typemicro-displays. This is made possible by designing the magnifier lenses70 to be approximately telecentric on the display side (i.e., chief raysnearly parallel to the optical axis of the system, which is itselfparallel to the display surface normal). It is known that doing soreduces perceived brightness falloff toward the corners of the display(which can be substantial with non-telecentric lenses). In embodiments1-7, the maximum chief ray angle (absolute value) on the display sidefor all of these embodiments is <3 degrees. Additionally, theembodiments described above are suitable for use with other types ofelectronic displays and micro-displays, for example, light emittingdiode displays such as organic light emitting diode displays, polymericlight emitting diode displays, etc.

Additionally, embodiments 1-7 employ vignetting at the front, eye sidesurface of the first element E₁. Vignetting stops some aberrated raysnear the edge of the pupil from reaching off-axis points in the imageplane. This increases off-axis image quality at the expense of reducedillumination in the corners of the image relative to that at the centerof the image (i.e., relative illumination). Vignetting in the corner ofthe image is between 25% and 35% for the embodiments described above.This is well within the (generally accepted) 30-40% vignetting that thehuman eye can tolerate before it becomes noticeable.

It is well known by those skilled in the art of magnifier design thatthe human eye can accommodate some degree of field curvature byeffectively refocusing (the eye) for different parts of the field. Theeye can also tolerate some (typically, lesser) degree of astigmatism.Traditionally, when the tangential and sagittal field curves all liewithin 1 diopter of the central focus, the image is reasonably welldefined over the field. Also, in the absence of astigmatism, a youngobserver can focus on the field edge and accommodate about 3 dioptersfor the center. In embodiments 1-7, the image is permitted to curvesomewhat, thereby facilitating the reduction of astigmatism in themagnifier lenses 70. The result is essentially just some degree of fieldcurvature (from the lenses) and the astigmatism associated with the PBS20. For the embodiments described above, the curvature of the fieldcorresponds to an accommodation of <0.6 diopters between the center andthe edge of the field.

The through-focus MTF plots shown in FIGS. 8-14 are polychromatic (equalweights of 510 nm, 560 nm, and 610 nm light) for the embodimentsdepicted in FIGS. 1-7, and Tables 1-7, respectively. The MTF plots areshown for 21 line pairs/mm, half the nyquist frequency for a displaywith 0.012 mm square pixels. Each MTF plot assumes a curved imagesurface with radius as given in the prescriptions of Tables 1-7.

It should be noted that for the embodiments in FIGS. 5-7 and Tables 5-7,respectively, the polychromatic MTF performance is substantially thesame for equal weights of 450 nm, 550 nm, and 650 nm. For theembodiments in FIGS. 1-4 and Tables 1-4, respectively, the polychromaticMTF performance drops somewhat for equal weights of 450 nm, 550 nm, and650 nm, but may be recovered quite well with a quick re-optimization.

TABLE 1 CLEAR SURF. APER. RADIUS THICKNESS INDEX V-NUMBER 6.00 DIAPHRAGM17.000  1 10.20* ASPHERE(1) 3.710 1.492 57.8 2 9.14   16.4892 1.900 38.62 −22.2252(2) 2.972 1.590 30.8 4 7.90 ASPHERE(1) 2.443 5 6.79 PLANO0.330 1.550 55.0 6 6.71 PLANO 4.635 7 4.93 PLANO 0.725 1.570 55.0 8 4.82−30.5417 *DO NOT EXCEED LENS LENGTH 8.582 NOTES: 1) ASPHERIC SURFACEDESCRIBED BY SAG EQUATION:${X(Y)} = {\frac{{CY}^{2}}{1 + \sqrt{1 - {\left( {k + 1} \right)C^{2}Y^{2}}}} + {DY}^{4} + {EY}^{6} + {FY}^{8} + {GY}^{10} + {HY}^{12}}$

SURF. 1 C =   0.1666667 D = −0.28952730E−03 F = −0.93959591E−06 k =  0.0000000 E =   0.90649168E−05 G =   0.35556391E−07 VERTEX RADIUS(1/C) = 6.0000 H = −0.57183989E−09 SURF. 4 C = −0.0897376 D =  0.79693786E−03 F =   0.24127936E−05 k =   0.0000000 E =  0.16847998E−05 G = −0.17226572E−06 VERTEX RADIUS (1/C) = −11.1436 H =  0.65623726E−08 2) DIFFRACTIVE SURFACE DESCRIBED BY PHASE EQUATION:${\Phi (Y)} = {\frac{2\quad \pi}{\lambda_{0}}\quad \left( {{C_{1}Y^{2}} + {C_{2}Y^{4}} + {C_{3}Y^{6}} + {C_{4}Y^{8}}} \right)}$

SURF. 3 λ₀ = 560 NM C₁ = −4.12013E−03 C₃ = −3.46267E−06 C₂ =  7.96815E−05 C₄ =   1.07025E−07

TABLE 2 CLEAR SURF. APER. RADIUS THICKNESS INDEX V-NUMBER 6.00 DIAPHRAGM17.000  1 10.20*    6.229 3.851 1.492 57.8 2 9.11 ASPHERE(1) 1.807 38.69 −13.0221(2) 2.946 1.590 30.8 4 8.14 ASPHERE(1) 2.594 5 6.82 PLANO0.330 1.550 55.0 6 6.74 PLANO 4.635 7 4.93 PLANO 0.725 1.570 55.0 8 4.82−30.5417 *DO NOT EXCEED LENS LENGTH 8.604 NOTES: 3) ASPHERIC SURFACEDESCRIBED BY SAG EQUATION:${X(Y)} = {\frac{{CY}^{2}}{1 + \sqrt{1 - {\left( {k + 1} \right)C^{2}Y^{2}}}} + {DY}^{4} + {EY}^{6} + {FY}^{8} + {GY}^{10} + {HY}^{12}}$

SURF. 2 C =   0.4044146 D =   0.52788255E−03 F =   0.48822016E−06 k =  0.0000000 E = −0.51777047E−05 G = −0.48083647E−07 VERTEX RADIUS (1/C)= 24.7271 H =   0.36767183E−09 SURF. 4 C = −0.1093386 D =  0.64198372E−03 F =   0.35968081E−05 k =   0.0000000 E =−0.11253640E−04 G = −0.21871596E−06 VERTEX RADIUS (1/C) = −9.1459 H =  0.74093706E−08 4) DIFFRACTIVE SURFACE DESCRIBED BY PHASE EQUATION:${\Phi (Y)} = {\frac{2\quad \pi}{\lambda_{0}}\quad \left( {{C_{1}Y^{2}} + {C_{2}Y^{4}} + {C_{3}Y^{6}} + {C_{4}Y^{8}}} \right)}$

SURF. 3 λ₀ = 560 NM C₁ = −4.06429E−03 C₃ = −3.73155E−06 C₂ =  7.15512E−05 C₄ =   1.62241E−07

TABLE 3 CLEAR SURF. APER. RADIUS THICKNESS INDEX V-NUMBER 6.00 DIAPHRAGM17.000  1 10.20* ASPHERE(1) 4.091 1.492 57.8 2 8.95   19.2401(2) 1.264 38.57 −39.0234 2.750 1.590 30.8 4 7.56 ASPHERE(1) 2.441 5 6.63 PLANO0.330 1.550 55.0 6 6.56 PLANO 4.635 7 4.92 PLANO 0.725 1.570 55.0 8 4.83−30.5417 *DO NOT EXCEED LENS LENGTH 8.105 NOTES: 5) ASPHERIC SURFACEDESCRIBED BY SAG EQUATION:${X(Y)} = {\frac{{CY}^{2}}{1 + \sqrt{1 - {\left( {k + 1} \right)C^{2}Y^{2}}}} + {DY}^{4} + {EY}^{6} + {FY}^{8} + {GY}^{10} + {HY}^{12}}$

SURF. 1 C =   0.1646063 D = −0.20370475E−03 F = −0.70916812E−06 k =  0.0000000 E =   0.86070374E−05 G =   0.24289232E−07 VERTEX RADIUS(1/C) = 6.0751 H = −0.31512663E−09 SURF. 4 C = −0.0603912 D =  0.95297402E−03 F =   0.62224391E−05 k =   0.0000000 E =−0.15864043E−04 G = −0.47132486E−06 VERTEX RADIUS (1/C) = −16.5587 H =  0.17717982E−07 6) DIFFRACTIVE SURFACE DESCRIBED BY PHASE EQUATION:${\Phi (Y)} = {\frac{2\quad \pi}{\lambda_{0}}\quad \left( {{C_{1}Y^{2}} + {C_{2}Y^{4}} + {C_{3}Y^{6}} + {C_{4}Y^{8}}} \right)}$

SURF. 2 λ₀ = 560 NM C₁ = −3.32269E−03 C₃ = −1.71275E−06 C₂ =  4.52118E−05 C₄ =   5.78513E−08

TABLE 4 CLEAR SURF. APER. RADIUS THICKNESS INDEX V-NUMBER 6.00 DIAPHRAGM17.000  1 10.20* ASPHERE(1) 4.292 1.492 57.8 2 8.55    8.1991(2) 1.349 38.38   21.6332 2.750 1.590 30.8 4 7.62 ASPHERE(1) 2.441 5 6.67 PLANO0.330 1.550 55.0 6 6.59 PLANO 4.635 7 4.93 PLANO 0.725 1.570 55.0 8 4.81−30.5417 *DO NOT EXCEED LENS LENGTH 8.393 NOTES: 7) ASPHERIC SURFACEDESCRIBED BY SAG EQUATION:${X(Y)} = {\frac{{CY}^{2}}{1 + \sqrt{1 - {\left( {k + 1} \right)C^{2}Y^{2}}}} + {DY}^{4} + {EY}^{6} + {FY}^{8} + {GY}^{10} + {HY}^{12}}$

SURF. 1 C =   0.1682086 D = −0.36386441E−03 F = −0.13188881E−05 k =  0.0000000 E =   0.12936727E−04 G =   0.50574451E−07 VERTEX RADIUS(1/C) = 5.945 H = −0.93964616E−09 SURF. 4 C = −0.0426814 D =  0.71989155E−03 F =   0.27592984E−05 k =   0.0000000 E =−0.41520397E−05 G = −0.20084234E−06 VERTEX RADIUS (1/C) = −23.4294 H =  0.85266176E−08 8) DIFFRACTIVE SURFACE DESCRIBED BY PHASE EQUATION:${\Phi (Y)} = {\frac{2\quad \pi}{\lambda_{0}}\quad \left( {{C_{1}Y^{2}} + {C_{2}Y^{4}} + {C_{3}Y^{6}} + {C_{4}Y^{8}}} \right)}$

SURF. 2 λ₀ = 560 NM C₁ = −3.74332E−03 C₃ =   4.01070E−06 C₂ =−5.34761E−05 C₄ = −4.14056E−08

TABLE 5 CLEAR SURF. APER. RADIUS THICKNESS INDEX V-NUMBER 6.00 DIAPHRAGM17.000  1  9.10* ASPHERE(1) 3.380 1.492 57.8 2 8.73 −104.3823 0.181 38.52    32.1466 1.449 1.583 30.1 4 7.57 ASPHERE(1) 1.053 5 7.99   6.9618 3.698 1.492 57.8 6 7.85 ASPHERE(1) 2.444 7 6.73 PLANO 0.3301.550 55.0 8 6.66 PLANO 4.635 9 4.95 PLANO 0.725 1.570 55.0 10  4.82 −28.7621 *DO NOT EXCEED LENS LENGTH 9.761 NOTES: 1) ASPHERIC SURFACEDESCRIBED BY SAG EQUATION:${X(Y)} = {\frac{{CY}^{2}}{1 + \sqrt{1 - {\left( {k + 1} \right)C^{2}Y^{2}}}} + {DY}^{4} + {EY}^{6} + {FY}^{8} + {GY}^{10} + {HY}^{12}}$

SURF. 1 C =   0.1582487 D =   0.0000000E+00 F =   0.0000000E+00 k =−1.2126760 E =   0.0000000E+00 G =   0.0000000E+00 VERTEX RADIUS (1/C) =6.3194 H =   0.0000000E+00 SURF. 4 C =   0.2284044 D =   0.0000000E+00 F=   0.0000000E+00 k = −0.7743398 E =   0.0000000E+00 G =   0.0000000E+00VERTEX RADIUS (1/C) = 4.3782 H =   0.0000000E+00 SURF. 6 C = −0.0868644D =   0.4399801E−03 F = −0.3529413E−06 k =   0.0000000 E =  0.4799854E−05 G =   0.8495183E−08 VERTEX RADIUS (1/C) = −11.5122 H =  0.0000000E+00

TABLE 6 CLEAR SURF. APER. RADIUS THICKNESS INDEX V-NUMBER 6.00 DIAPHRAGM17.000  1  9.10* ASPHERE(1) 3.188 1.492 57.8 2 8.69   95.4845 0.335 38.50   26.9536 1.280 1.583 30.1 4 7.66 ASPHERE(1) 0.744 5 7.82 7.16933.314 1.492 57.8 6 7.61 ASPHERE(1) 2.657 7 6.56 PLANO 0.330 1.550 55.0 86.49 PLANO 4.635 9 4.94 PLANO 0.725 1.570 55.0 10  4.82 −28.9000 *DO NOTEXCEED LENS LENGTH 8.861 NOTES: 2) ASPHERIC SURFACE DESCRIBED BY SAGEQUATION:${X(Y)} = {\frac{{CY}^{2}}{1 + \sqrt{1 - {\left( {k + 1} \right)C^{2}Y^{2}}}} + {DY}^{4} + {EY}^{6} + {FY}^{8} + {GY}^{10} + {HY}^{12}}$

SURF. 1 C =   0.1627657 D = −0.9597174E−05 F =   0.8515111E−07 k =−1.0784800 E =   0.6443622E−07 G = −0.8389589E−09 VERTEX RADIUS (1/C) =6.1438 H =   0.0000000E+00 SURF. 4 C =   0.2147075 D =   0.0000000E+00 F=   0.0000000E+00 k = −0.9062283 E =   0.0000000E+00 G =   0.0000000E+00VERTEX RADIUS (1/C) = 4.6575 H =   0.0000000E+00 SURF. 6 C = −0.0832591D =   0.6436675E−03 F = −0.3216570E−06 k =   0.0000000 E =  0.7271238E−05 G =   0.2184924E−07 VERTEX RADIUS (1/C) = −12.0107 H =  0.0000000E+00

TABLE 7 CLEAR SURF. APER. RADIUS THICKNESS INDEX V-NUMBER 6.00 DIAPHRAGM17.000  1  9.10* ASPHERE(1) 3.339 1.492 57.8 2 8.74 −224.8469  0.210 38.54    26.8436 1.423 1.583 30.1 4 7.61 ASPHERE(1) 0.939 5 7.85ASPHERE(1) 3.574 1.492 57.8 6 7.71  −16.4096 2.444 7 6.64 PLANO 0.3301.550 55.0 8 6.56 PLANO 4.635 9 4.91 PLANO 0.725 1.570 55.0 10  4.81 −28.7621 *DO NOT EXCEED LENS LENGTH 9.485 NOTES: 3) ASPHERIC SURFACEDESCRIBED BY SAG EQUATION:${X(Y)} = {\frac{{CY}^{2}}{1 + \sqrt{1 - {\left( {k + 1} \right)C^{2}Y^{2}}}} + {DY}^{4} + {EY}^{6} + {FY}^{8} + {GY}^{10} + {HY}^{12}}$

SURF. 1 C =   0.1609088 D =   0.0000000E+00 F =   0.0000000E+00 k =−1.3568420 E =   0.0000000E+00 G =   0.0000000E+00 VERTEX RADIUS (1/C) =6.2147 H =   0.0000000E+00 SURF. 4 C =   0.2735529 D =   0.0000000E+00 F=   0.0000000E+00 k = −1.5674930 E =   0.0000000E+00 G =   0.0000000E+00VERTEX RADIUS (1/C) = 3.6556 H =   0.0000000E+00 SURF. 5 C =   0.2075765D = −0.2473807E−02 F =   0.6771738E−06 k =   0.0000000 E =−0.1801932E−04 G = −0.1057451E−06 VERTEX RADIUS (1/C) = 4.8616 H =  0.0000000E+00

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the scope of theinvention.

What is claimed is:
 1. A magnifier lens comprising in order from an eyeside: a first positive power meniscus lens element having an eye sidesurface and an object side surface, at least one of the eye side surfaceand the object side surface being aspheric; and a second positive powerlens element having an aspheric object side surface convex toward theobject side and an eye side surface, wherein at least one of the objectside surface of the first positive power meniscus element and the eyeside surface of the second positive power element is diffractive.
 2. Thelens of claim 1, wherein the second positive power lens element ismeniscus.
 3. The lens of claim 2, wherein the second positive powermeniscus lens element is concave toward the eye side.
 4. The lens ofclaim 1, wherein the second positive power lens element is bi-convex. 5.The lens of claim 1, wherein the first positive power meniscus lenselement is convex toward the eye side.
 6. An optical system comprisingin order from an eye side: a first positive power meniscus lens elementhaving an eye side surface and an object side surface, at least one ofthe eye side surface and the object side surface being aspheric; asecond positive power lens element having an aspheric object sidesurface convex toward the object side and an eye side surface, whereinat least one of the object side surface of the first positive powermeniscus element and the eye side surface of the second positive powerelement is diffractive; and an object to be viewed.
 7. The opticalsystem of claim 6, wherein a back focal length in air from the objectside surface of the second positive power lens element to the object tobe viewed is no less than about 7.7 mm.
 8. The optical system of claim6, further comprising: a cover glass positioned on an eye side of theobject to be viewed; and a beam splitter positioned between the objectside surface of the second positive power lens element and the coverglass, wherein the object side surface of the second positive power lenselement is positioned about 8.1 mm from the object to be viewed.
 9. Theoptical system of claim 6, wherein the object to be viewed is anelectronic display.
 10. The optical system of claim 9, wherein theelectronic display is a liquid crystal display.
 11. The optical systemof claim 9, wherein the electronic display has a full diagonal ofapproximately 6 mm or less.
 12. The optical system of claim 9, whereinthe electronic display is a micro-display.
 13. The optical system ofclaim 9, wherein the electronic display is a light emitting diodedisplay.
 14. The optical system of claim 13, wherein the light emittingdiode display is an organic light emitting diode display.
 15. Theoptical system of claim 13, wherein the light emitting diode display isa polymeric light emitting diode display.
 16. The optical system ofclaim 6, the first and second lens elements comprising a magnifier lenshaving an object side positioned proximate to the object to be viewed,wherein the magnifier lens is adapted to be approximately telecentric onthe object side of the magnifier lens.
 17. The optical system of claim6, wherein a length in air from any location on the object side surfaceof the second positive power lens element to the object to be viewed isno less than about 7.7 mm.
 18. A magnifier lens comprising in order froman eye side: a first positive power lens element having an asphericsurface; and a second positive power lens element having an asphericsurface, the second positive power lens element having an object sidesurface, the object side surface having a most object side point, themagnifier lens having an effective focal length, wherein a distance fromthe most object side point on the object side surface of the secondpositive power lens element to an object to be viewed is greater than0.38 times the effective focal length of the magnifier lens.
 19. Themagnifier lens of claim 18, the magnifier lens having a back focallength in air, wherein the back focal length in air is greater than orequal to 7.7 mm.
 20. The magnifier lens of claim 18, the magnifier lenshaving an eye relief, wherein the eye relief is greater than theeffective focal length.
 21. The magnifier lens of claim 20, wherein theeye relief is greater than 1.3 times the effective focal length.
 22. Themagnifier lens of claim 18, the magnifier lens having a magnification,wherein the magnification is at least 15×.
 23. The magnifier lens ofclaim 22, wherein the magnification is greater than 19×.
 24. Themagnifier lens of claim 18, the magnifier lens having an eye relief,wherein the eye relief is at least 17 mm.
 25. The magnifier lens ofclaim 18, the magnifier lens having an apparent field of view, whereinthe apparent field of view is at least +/−10 degrees.
 26. The magnifierlens of claim 18, wherein the first and second positive lens elementsare made from plastic.
 27. The magnifier lens of claim 18, furthercomprising: a negative power lens element positioned between the firstand second positive power lens elements, the negative power lens elementhaving an aspheric surface.
 28. The magnifier lens of claim 27, whereinthe negative power lens element is made from plastic.
 29. The magnifierlens of claim 27, wherein at least two of the aspheric surfaces aresimple conics.
 30. The magnifier lens of claim 29, the first positivepower lens element having an eye side surface, the eye side surfacebeing the simple conic.
 31. The magnifier lens of claim 29, the secondnegative power lens element having a object side surface, the objectside surface being the simple conic.
 32. The magnifier lens of claim 27,wherein the second negative power lens element is meniscus.
 33. Themagnifier lens of claim 27, wherein the third positive power lenselement is bi-convex.
 34. The magnifier lens of claim 27, the magnifierlens having a back focal length in air, wherein the back focal length isgreater than 0.38 times the effective focal length.
 35. The magnifierlens of claim 27, the magnifier lens having a back focal length in air,wherein the back focal length is greater than 0.59 times the effectivefocal length.
 36. The magnifier lens of claim 27, each lens element ofthe magnifier lens having a center thickness and an edge thickness,wherein a ratio of center thickness to edge thickness of each lenselement is between 0.5 and 2.0.
 37. The magnifier lens of claim 27, themagnifier lens having a total thickness from the eye side surface of thefirst lens element to a surface of a viewable object, wherein the totalthickness is less than 17.9 mm.
 38. The magnifier lens of claim 27, themagnifier lens having a total thickness from the eye side surface of thefirst lens element to a surface of a viewable object, wherein the totalthickness is less than 1.40 times the effective focal length.
 39. Amagnifier lens comprising in order from an eye side: a first positivepower lens element having an aspheric surface and a second positivepower lens element having an aspheric surface, the magnifier lens havinga back focal length in air, wherein the back focal length of themagnifier lens in air is greater than 5 mm and at least one of thepositive power lens elements includes a diffractive surface.
 40. Themagnifier lens of claim 39, the first positive power lens element havingan object side surface, wherein the diffractive is on the object sidesurface of the first positive power lens element.
 41. The magnifier lensof claim 39, the second positive power lens element having an eye sidesurface, wherein the diffractive is on the eye side surface of thesecond positive power lens element.
 42. The magnifier lens of claim 39,the second positive power lens element having an object side surface,wherein the object side surface of the second positive power lenselement is convex toward the object side.
 43. The magnifier lens ofclaim 42, wherein the object side surface of the second positive powerlens element is aspheric.
 44. The magnifier lens of claim 39, whereinthe first positive power lens element is meniscus.
 45. The magnifierlens of claim 39, wherein the second positive power lens element isbi-convex.
 46. The magnifier lens of claim 39, the diffractive surfacehaving zone spacing, wherein the zone spacing is at least 20 microns.47. The magnifier lens of claim 18, the magnifier lens having an objectside positionable proximate to an object to be viewed, wherein themagnifier lens is adapted to be approximately telecentric on the objectside of the magnifier lens.
 48. The magnifier lens of claim 18, themagnifier lens having a back focal length in air, wherein the back focallength is greater than 0.38 times the effective focal length.
 49. Themagnifier lens of claim 18, the magnifier lens having a back focallength in air, wherein the back focal length is greater than 0.59 timesthe effective focal length.
 50. The magnifier lens of claim 18, eachlens element of the magnifier lens having a center thickness and an edgethickness, wherein a ratio of center thickness to edge thickness of eachlens element is between 0.9 and 2.1.
 51. The magnifier lens of claim 18,the magnifier lens having a total thickness from the eye side surface ofthe first lens element to a surface of a viewable object, wherein thetotal thickness is less than 17.0 mm.
 52. The magnifier lens of claim18, the magnifier lens having a total thickness from the eye sidesurface of the first lens element to a surface of a viewable object,wherein the total thickness is less than 1.33 times the effective focallength.
 53. A magnifier lens comprising in order from an eye side: afirst positive power lens element having an aspheric surface; and asecond positive power lens element having an aspheric surface, themagnifier lens having a back focal length in air, an eye relief, and aneffective focal length, wherein the back focal length of the magnifierlens in air is greater than 5 mm and the eye relief is greater than theeffective focal length.
 54. The magnifier lens of claim 53, wherein theeye relief is greater than 1.3 times the effective focal length.
 55. Amagnifier lens comprising in order from an eye side: a first positivepower lens element having an aspheric surface; and a second positivepower lens element having an aspheric surface, the magnifier lens havinga back focal length in air and an effective focal length, wherein theback focal length of the magnifier lens in air is greater than 5 mm andwherein the back focal length is greater than 0.3 8 times the effectivefocal length.
 56. The magnifier lens of claim 55, wherein the back focallength is greater than 0.59 times the effective focal length.
 57. Amagnifier lens comprising in order from an eye side: a first positivepower lens element having an aspheric surface; a negative power lenselement having an aspheric surface; and a second positive power lenselement having an aspheric surface, the magnifier lens having a backfocal length in air and an effective focal length, wherein the backfocal length of the magnifier lens in air is greater than 5 mm and theback focal length is greater than 0.38 times the effective focal length.58. The magnifier lens of claim 57, wherein the back focal length isgreater than 0.59 times the effective focal length.
 59. A magnifier lenscomprising in order from an eye side: a first positive power lenselement having an aspheric surface; a negative power lens element havingan aspheric surface; and a second positive power lens element having anaspheric surface, the magnifier lens having a back focal length in air,an effective focal length, and a total thickness from the eye sidesurface of the first lens element to a surface of a viewable object,wherein the back focal length of the magnifier lens in air is greaterthan 5 mm and the total thickness is less than 1.40 times the effectivefocal length.
 60. A magnifier lens comprising in order from an eye side:a first positive power lens element having an aspheric surface; and asecond positive power lens element having an aspheric surface, themagnifier lens having a back focal length in air, an effective focallength, and a total thickness from the eye side surface of the firstlens element to a surface of a viewable object, wherein the back focallength of the magnifier lens in air is greater than 5 mm and the totalthickness is less than 1.33 times the effective focal length.